1. Field of the Invention
The present invention relates to an apparatus and method for recording and/or reproducing a digital signal, and more particularly to such an apparatus and method suitable for use in recording and/or reproducing a digital signal transferred from a computer or the like.
2. Description of the Prior Art
In practice, data stored in a hard disk or the like of a computer may be transferred to and recorded by a data streamer (data-recorder) once a day so as to protect the data or back up the same.
For this operation, or as a data recorder, analog audio tape recorders have been conventionally used in many cases. However, analog tape recorders have disadvantages in that they need an excessive amount of a recording medium or magnetic tape for recording and operate at a quite low data transferring rate upon recording, so that it takes too much time to transfer and record such data information. Moreover, analog tape recorders have problems, e.g. the starting point of a desired portion of the recorded data information cannot be rapidly searched for, and so on.
Thus, to overcome the above-mentioned problems, it is thought to utilize a helical-scan type DAT (digital audio tape recorder) using a rotary head, that is, a so-called recently commercialized DAT as a data recorder. Such data recorders utilizing a DAT are described in U.S. patent application Ser. Nos. 133,010 filed Dec. 15, 1987, 177,624 filed Apr. 5, 1988, 210,229 filed June 23, 1988 and 220,028 filed July 15, 1988, by the same assignee of the present application.
To utilize the DAT as a data recorder, data transferred from a host computer is transformed in accordance with a DAT format before recording. In the DAT format, one frame is made up of two oblique tracks formed by one rotation of two heads each having a different azimuth angle with respect to the tape. 16-bit PCM audio data, which has been interleaved, and auxiliary sub-data are recorded in this one frame area as a unit. During recording, there are formed in each track a main area for recording the PCM data and a sub-area for recording the sub-data.
With the DAT as described above, when another signal is to be recorded on a previously recorded recording medium or tape, previously recorded signals are erased by recording new signals thereover, that is, by a so-called overwriting, without using an erasing head. Therefore, if overwriting is not normally effected, for example, due to clogging of the head or the like, there is the possibility that a part of the previously recorded signals may remain unerased. Also, if the tape loses contact with the heads for an instant, previously recorded signals may remain unerased. Either problem causes a data error referred to as "drop-in".
To avoid this data error, in the DAT format, an error detecting code is added to each of the main area and the sub-area of each track in which signals are recorded, so as to detect an unerased portion, if any, in the track as an error.
In the DAT format as described above, the main area and the sub-area of one track are respectively provided with the error detecting code so that the drop-in can be detected in the concerned area. However, even though such an error detecting code is added, in the event that previously recorded signals in an entire main area or an entire sub-area remain unerased, the drop-in cannot be detected if the error detecting code in the concerned area is considered to be normal.
If a signal to be recorded is an audio signal, signals remaining in the unerased portion can be removed by positional correlation or the like. However, when the DAT is utilized as a data recorder, there is generally no positional correlation of data. Moreover, when the DAT is used as a data recorder, it is required to record and reproduce data more exactly than for audio signals.